The present invention relates to methods and devices for attenuating an optical signal. The present invention more particularly relates to methods and devices for variably attenuating an optical signal within an optical network or a micro-electro-mechanical system (MEMS).
In the modern optical network there are many places where there are requirements to attenuate the optical power of a signal. The prior art includes methods and devices that enable transmission and attenuation of a light beam from an input wave guide and to an output wave guide by aiming and mis-aiming the light beam in a direct transmission from the input wave guide and into the output wave guide. The prior art additionally includes devices that employ a mirror to reflect the light beam from an input wave guide, such as an optical fiber, and into an output wave guide, where the output wave guide may also be an optical fiber. These prior art techniques, however, exhibit highly non-linear relationships between an actuator control signal and a resulting attenuation, as measured in decibels, of a transmission of the light beam, wherein the sensitivity of the effected attenuation is often undesirably high in response to small variations in the control signal.
A long felt need therefore exists to provide a method and device for variably attenuating an optical signal in a more linear relationship between the actuator control signal and the resulting optical signal attenuation, where the attenuation is measured in decibels. Additionally, a MEMS based variable optical attenuator that provides a finer and more precise control over the optical attenuation of the optical signal would satisfy certain needs of optical systems architects and improve the performance of an optical communications network.
It is an object of the present invention to provide a method of variable optical attenuation with improved performance.
It is an object of certain preferred embodiments of the present invention to provide a variable optical attenuator, or VOA, having improved characteristics.
It is an alternate object of certain preferred embodiments of the present invention to provide a VOA that attenuates an optical signal with improved linearity.
It is a still alternate object of certain preferred embodiments of the present invention to provide a VOA that attenuates an optical signal with improved resolution.
It is another object of certain preferred embodiments of the present invention to provide a VOA that attenuates an optical signal with improved accuracy.
It is yet another object of certain preferred embodiments of the present invention to provide a VOA that attenuates an optical signal with decreased power requirements.
The invention is a variable optical attenuator and method of use thereof for attenuating an optical signal by directing the transmission of a light beam into a photonic component along a trajectory, where the trajectory lies on a receiving face of the photonic component and has geometric components in at least two dimensions. The method of the preferred embodiment of the present invention comprises the generation of a non-linear trajectory of a light beam on an output photonic component by directing the light beam in two dimensions between an input photonic component and the output photonic component. The non-linear trajectory is formed by changing the direction of the light beam and thereby changing an alignment of the light beam with regard to the receiving face of the output photonic component.
The method of the present invention linearizes the optical-loss-versus-actuation curve for the invented VOA, in which attenuation of an optical signal is based on a misalignment of the light beam from, for example, as transmitted from the receiving face 14 of the first optical fiber to the receiving face of the second optical fiber.
Prior art VOA""s based on this misalignment method generate variable optical losses by moving a spot of the light beam along the trajectory therefore upon the receiving face of the photonic component. The spot is the intersection, or strike, of the light beam on the receiving face. The spot includes a center point (peak power density point) of the light beam. In the prior art attenuation is achieved by locating strike and the center point away from a center of the core of an output optical fiber along a linear trajectory, i.e. within a straight line. The disadvantage of the prior art is that the loss versus position of the image is a highly non-linear (approximately quadratic) relationship due to the wave guide properties of single mode fibers. This means that at higher attenuation settings, the actual attenuation is highly sensitive to the spot position which puts severe constraints on the control of the spot position.
The method of the present invention comprises the steps of moving the light beam to locate the spot on the face of the receiving fiber along a two-dimensional trajectory, instead of along a straight line. The two-dimensional trajectory can be designed such that the overall loss-versus-trajectory-position is linearized significantly compared to the quadratic relation when moving along a straight line, reducing the sensitivity to position uncertainty.
A trajectory path of the light beam is established on a receiving face of the photonic component by dynamically altering the direction of the light beam in at least two dimensions. A trajectory path is created in certain preferred embodiments of the method of the present invention wherein the relationship between the distance traveled by the light beam within the trajectory and the resulting attenuation, as expressed in decibels, is more linear as compared with the prior art.
A trajectory path of the light beam can alternately or additionally be chosen as to improve the linearity between a control signal and a resulting attenuation, as expressed in decibels, as the control signal is varied. The method of the present invention is not limited to actuators that act on a photonic component in linear or near relationships between the control signal and a variable force, load or other output of the attenuator directed to a photonic component, such as an optical fiber or a mirror.
A photonic component as defined herein includes mirrors, prisms, wave guides, optical fibers, lenses, collimators, and other suitable photonic and optical devices and elements known in the art. A wave guide as defined herein includes optical fibers, planar wave guides, and other suitable channels for optical signal and light energy transmission known in the art.
A first preferred embodiment of the present invention includes an input wave guide, an output wave guide and an actuator. The actuator is operatively coupled, in alternate preferred embodiments, to either the input wave guide or the output wave guide, or both. The light beam travels from the input wave guide and towards the output wave guide. The actuator moves one or more wave guides to which it is operatively coupled within at least two degrees of freedom, or in two dimensions, to form a trajectory of the light beam having geometric components of at least two dimensions. The at least two-dimensional trajectory enables the attenuation, as expressed in decibels, of the transmission of the light beam with an increased linearity, over the prior art, in relation to a control or driving signal supplied to the actuator. The control signal is, or comprises, in various preferred embodiments of the present invention, an electrical current, a voltage, power, or other suitable control signal parameters, qualities or content known in the art. Certain alternate preferred embodiments include optical fibers as input and/or output wave guides.
A second preferred embodiment of the present invention includes an input wave guide, an output wave guide, a mirror, a mirror actuator and an output collimator. The output collimator may be or comprise an optical lens, a spherical lens, an aspherical lens, a ball lens, a GRIN lens, a C-lens, a lens system, or another suitable collimating element known in the art. The output collimator is positioned between the mirror and the output wave guide. The light beam travels from the input wave guide to the mirror and is reflected from the mirror and focused through the output collimator and into the output wave guide. The mirror may be a substantially flat mirror or another suitable mirror known in the art. The position of the mirror determines the variable optical attenuation of the light beam transmission from the input wave guide to the output wave guide. The mirror actuator is operatively coupled to the mirror. The mirror actuator moves the mirror within at least two degrees of freedom, or in two dimensions, to form a trajectory of the light beam wherein the trajectory has geometric components of at least two dimensions. The at least two-dimensional trajectory enables the attenuation of the light beam transmission with an increased linearity, over the prior art, in relation to a driving signal supplied to the actuator. The second preferred embodiment may include optical fibers as wave guides. The second preferred embodiment may optionally include an input collimator. The input collimator is positioned between the input wave guide and the mirror. The light beam travels from the input wave guide to the mirror via the input collimator, and is reflected from the mirror and toward the output wave guide via the output collimator.
A third preferred embodiment of the present invention includes a mirror, a mirror actuator, and a dual optical fiber collimator having a lens and an input optical fiber and an output optical fiber. The dual fiber collimator lens may be or comprise one or more collimating elements or focusing elements, such as an optical lens, a spherical lens, an aspherical lens, a ball lens, a GRIN lens, a C-lens, a lens system, or another suitable collimating element known in the art. The dual fiber collimator lens is positioned relative to the mirror and the input and output optical fibers to collimate the light beam as the light beam travels toward the mirror and to focus the light beam as the light beam travels from the mirror. The light beam travels from the input optical fiber to the mirror via the input collimator component, and is reflected from the mirror and toward the output optical fiber via the output collimator component. The mirror actuator moves the mirror within at least two degrees of freedom, or in two dimensions, to form a trajectory of the light beam wherein the trajectory has geometric components of at least two dimensions. The at least two-dimensional trajectory enables the attenuation of the light beam transmission with an increased linearity, over the prior art, in relation to a driving signal supplied to the actuator.
Other objects, features, and advantages of the present invention will be apparent from the accompanying drawings and from the detailed description which follows below.